This invention relates to the detection and classification of metal objects such as buried explosive mines in a minefield, and more particularly to an improved mine detection and display system in combination with an automotive vehicle.
Various methods and apparatus for the detection of land mines have been employed and proposed. These have included a variety of sensors such as magnetometers, electromagnetic transmitters and receivers, sonic devices, devices using electron paramagnetic resonance signals, and other sensors. Systems using such sensors have demonstrated that mine detection is feasible, however the signals generated have generally been difficult to interpret and accordingly the degree of success has varied considerably with the skill of the operator.
In the case of portable instruments, the signals are usually delivered to earphones and vary in pitch or intensity and the operator classifies the detection on this basis, using experience as a guide. A method that has been tried, in an effort to avoid reliance on audible interpretation, records voltage values in numerical form on a paper tape and the operator converts the numbers mentally into somewhat of an "image." Still another method is to record the analog value of the signal in the form of a "signature" trace on paper tape and having the operator interpret the shape and intensity variations, as well as the signal polarity, to classify the signal recorded as to location, depth, size, etc. of a detected object. The foregoing methods operate essentially in real time and allow a classification to be made as a mine search progresses.
The principal objection to the methods cited is the difficulty in analyzing and interpreting the audible or recorded signals. In the case of audible signals from a total field magnetometer, the type best suited for detecting the ferrous components of a land mine, no distinction can be made by the operator as to magnetic polarity. Inasmuch as magnetic polarity induced by the earth's magnetic field can be of considerable value in classifying a detected object as to size, shape, and particularly orientation, the use of audible interpretation is severely limited. The use of paper strip recorders, while giving some indications of polarity, are deficient in presenting a display from which the operator can derive a ready feel of geographic relationship correlating the tracing to the area being searched.